XAMPP stores Apache configuration in two files located at C:\xampp\apache\conf\httpd.conf and C:\xampp\apache\conf\httpd-vhosts.conf. Use your text editor to edit those (and set the default editor as notepad++ for .conf extensions). Lines starting with a # sign are comments. Remember that Linux uses /‘s for folders while Windows use \‘s. Apache wants you to use /‘s regardless of what operating system you have.
You may want to adjust some settings for PHP, but XAMPP comes with most of that already setup for you. PHP is configured in C:\xampp\php\php.ini. There is a file called php.ini-development also located there that is intended for development environments. You can replace php.ini with it to get all the message reporting that it offers.